Design for X Dr Jane Marshall Product Excellence using 6 Sigma Module PEUSS 2012/2013 Design for X Page 1 Objectives of the session Introduce Design for X Discuss Specific Design for X methods PEUSS 2012/2013 Design for X Page 2 1
Design for X Concurrent engineering is a contemporary approach to DFSS. DFX techniques are part of detail design To improve: life-cycle cost; quality, increased design flexibility, and increased efficiency and productivity Benefits include: competitiveness measures, improved decision-making, and enhanced operational efficiency. X in DFX is made up of two parts: life-cycle processes x and performance measure (ability) (Huang 1996). Effective approach to implement concurrent engineering. System design PEUSS 2012/2013 Design for X Page 3 System design Systems and its characteristics System is an interrelated set of components, with identifiable boundary, working together for some purpose A system has nine characteristics: Components----------------------Subsystems Interrelated components A boundary A purpose An environment Interfaces Input Output Constraints PEUSS 2012/2013 Design for X Page 4 2
Input Environment Interface Components Output Boundary Interrelationship Design for X PEUSS 2012/2013 Page 5 System characteristics A component an irreducible part or aggregation of parts that make up a system, also called a subsystem Interrelated components Dependence of one subsystem on one or more subsystems Boundary The line that marks the inside and outside of a system and that sets off the system form its environment PEUSS 2012/2013 Design for X Page 6 3
System characteristics Purpose The overall goal or function of a system Environment Everything external to a system that interacts with the system Interface Point of contact where a system meets its environment or where subsystems meet each other. PEUSS 2012/2013 Design for X Page 7 System characteristics Constraint Input Output A limit to what a system can accomplish Whatever a system takes from its environment in order to fulfill its purpose Whatever a system returns from its environment in order to fulfill its purpose PEUSS 2012/2013 Design for X Page 8 4
Logical and Physical system description Logical system description Description of a system that focuses on the system function and purpose without regard to how the system will physically implemented Physical system description Description of a system that focuses on the how the system will be materially constructed PEUSS 2012/2013 Design for X Page 9 Important system concepts Decomposition Modularity Coupling Cohesion PEUSS 2012/2013 Design for X Page 10 5
Decomposition Is the process of breaking down a system into smaller components in order to: Focus on one area at a time Concentrate one component pertinent to one group of users Build different components at independent times PEUSS 2012/2013 Design for X Page 11 Modularity and Coupling Modularity Dividing a system up into chunks or modules of a relatively uniform size. To Simplify the redesign and rebuild process Coupling The extent to which subsystems depend on each other. Subsystem should be independent as possible. If one subsystem fails and other subsystem are highly dependent on it, then the other will either fail themselves or have problems functioning PEUSS 2012/2013 Design for X Page 12 6
Cohesion A cohesion is the extent to which a subsystem performs a single function. PEUSS 2012/2013 Design for X Page 13 Design for X tools Design for Manufacture and Assembly; Design for Reliability; Design for Maintainability; Design for Serviceability; Design for the Environment; Design for Life Cycle Cost; Etc. PEUSS 2012/2013 Design for X Page 14 7
Design for manufacture and assembly Consider during concept stage to reduce cost of redesign later Involvement of manufacturing engineers and supply chain management at concept phase Involve investigating waste Reducing number of standalone parts DFA time identifies cost of assembly and efficiency Investigate alternatives through experimentation Error-proofing poke-yoke PEUSS 2012/2013 Design for X Page 15 Design for Reliability Analyse load-strength relationship Design out inherent weaknesses Analyse potential failure mechanisms and remove or accommodate Analyse potential failure modes past data suppliers history Plan for reliability improvement Plan correct testing PEUSS 2012/2013 Design for X Page 16 8
What is Reliability? Quality over a period of time The ability of an item to perform a required function under stated conditions for a stated period of time. Reliability is an aspect of engineering uncertainty and therefore measured using probability PEUSS 2012/2013 Design for X Page 17 Why is reliability important? Costs of unreliability or unavailability Safety Competitiveness Examples: Airline costs Automotive reputation Military equipment availability PEUSS 2012/2013 Design for X Page 18 9
Why do products fail? Design inherently incapable Item overstressed Variation Wear-out Specification, design or coding errors Noise Interaction PEUSS 2012/2013 Design for X Page 19 How do Products fail? Discuss how products can fail? Choose different product types and give ideas for how they may fail? PEUSS 2012/2013 Design for X Page 20 10
Wear-out and Over-stress OVER-STRESS Fracture Yield Thermal Electrostatic discharge WEAR-OUT Fatigue Creep Erosion Corrosion PEUSS 2012/2013 Design for X Page 21 Electronic component failure examples Mechanical failure PCB PTH barrel crack Chip capacitor overstress Solder joint fatigue Chip resistor BGA active device PEUSS 2012/2013 Design for X Page 22 11
Corrosion Galvanic corrosion Fretting Corrosion Erosion Corrosion PEUSS 2012/2013 Design for X Page 23 Load and strength Load - Key Characteristic of interest in environment Temperature / Pressure Vibration / Humidity Strength - Key characteristic of interest in manufactured product Tensile Strength Current Rating Propagation Delay PEUSS 2012/2013 Design for X Page 24 12
Requirements & Environment - Engine Controls Typical Civil Engine environment Temperature extremes operating -55 to 100 non-operating -65 to 125 Vibration extremes low frequency <5g general blade passing Typical environment much more benign Service requirements 20g 50g Life 25 yrs 100,000 hrs operating Reliability 30,000 hours MTBF (33 failures/million hrs) FADEC Reliability Requirements In a Safety Critical Harsh Environment Application PEUSS 2012/2013 Design for X Page 25 Load and strength Generally failures occur if Load exceeds Strength PEUSS 2012/2013 Design for X Page 26 13
Load and strength Probability Load Strength No overlap of distributed values.. No failures PEUSS 2012/2013 Design for X Page 27 Load and strength Failure Probability Load Strength PEUSS 2012/2013 Design for X Page 28 14
Over-stress Load Strength Stress PEUSS 2012/2013 Design for X Page 29 Wear-out Load Strength Stress PEUSS 2012/2013 Design for X Page 30 15
Bathtub curve Hazard function Useful Life Infant Mortality Time Wear Out PEUSS 2012/2013 Design for X Page 31 Design for Reliability Aim to maximise reliability during service life by: Measurement & control of manufacturing quality / screening Optimized design & build process to improve intrinsic reliability Assure no systematic faults present in product Provide sufficient margin to meet life requirements PEUSS 2012/2013 Design for X Page 32 16
Early - life Hazard function Useful Life Time Infant Mortality/early life Wear Out PEUSS 2012/2013 Design for X Page 33 Early Life Failures Environmental Stress Screening Sometimes called burn-in electronic components Stresses that cause defective production items which pass other tests to fail Normally 100% test but can be done for batches HASS high combined stresses Test time shorter than ESS Cheaper PEUSS 2012/2013 Design for X Page 34 17
Early-life failures Quality in Manufacture Screening Effectiveness Service Life e.g. 20 Years Life Margin Hazard function Reliability Perceived Quality Time Life Failures PEUSS 2012/2013 Design for X Page 35 Early-life failures Too little product screening Service Life e.g. 20 Years Life Margin Screening Effectiveness Degraded Reliability Increased Low Hour Failures Improved 1st Time Pass Yield PEUSS 2012/2013 Design for X Page 36 18
Early-life failures Too much product screening Service Life e.g. 20 Years Life Margin Screening Effectiveness Higher Service Reliability Reduced Low Hour Failures Reduced 1st Time Pass Yield Reduced Life Margin PEUSS 2012/2013 Design for X Page 37 Screening effectiveness At what point is Manufacturing Quality measured? Following screening?. following x hours in service? Processes optimised to just pass ESS? Quality engineers aware of early life (service) failure? How well is E.S.S. Effectiveness measured? Failures being detected during ESS? What type of failure, at what point and in which test..? Optimised cycles, levels,etc? Measures of performance? PEUSS 2012/2013 Design for X Page 38 19
Product screening the answer? Service Life Improved Quality in Manufacture Improved Build Quality More Stringent Quality Control Less Reliance on Screening Higher Service Reliability Reduced Low Hour Failures Improved 1st Time Pass Yield Increased Life Margin PEUSS 2012/2013 Design for X Page 39 Useful- life Hazard function Useful Life Infant Mortality Time Wear Out PEUSS 2012/2013 Design for X Page 40 20
Useful- life Characterised by failures occurring randomly over time Due to non-systematic, minor anomalous process variations, for example: Marginal design / tolerance build-up Random periods of reduced manufacturing process control Component part batch problems Maintenance induced failure PEUSS 2012/2013 Design for X Page 41 Minimising failures during useful life Learning (and using) lessons from current products Determine those factors that have a significant effect on product reliability by analysing in-service with manufacturing data. Root Cause analysis of service issues enables generic process improvements in design and manufacture PEUSS 2012/2013 Design for X Page 42 21
Wear-out Hazard function Useful Life Infant Mortality Time Wear Out PEUSS 2012/2013 Design for X Page 43 Wear-out Characterised by failure mechanisms broadly repeated across a product type, often following a similar period of use. Due to systematic weak links in design / manufacture. Processes that consistently stress product during Manufacture Design / Selection of inappropriate parts or function Incompatibility between design and manufacturing capability Not necessarily an end of life issue Could occur at any point during product life PEUSS 2012/2013 Design for X Page 44 22
Wear-out - solutions How can systematic problems be detected prior to use? Physics of Failure (PoF) analysis, Finite Element Analysis, Design Of Experiments, Reliability Enhancement Testing (RET) PEUSS 2012/2013 Design for X Page 45 Design for Reliability Design for useful life Design out inherent weaknesses using tools such as: FMECA Fault tree analysis (FTA) Physics of Failure ESS Finite element analysis Development Testing Data analysis PEUSS 2012/2013 Design for X Page 46 23
Product life cycle Design Use Field data analysis FMECA, FTA, PoF,RBD FE,accelerated life test FRACAS Development Development Test Test ESS, Burn-in Manufacture SPC PEUSS 2012/2013 Design for X Page 47 Design for maintainability To minimise: The downtime for maintenance, user and technician maintenance time, personnel injury resulting from maintenance tasks, cost resulting from maintainability features, and logistics requirements for replacement parts, backup units, and personnel Maintenance actions can be preventive, corrective, or recycle and overhaul PEUSS 2012/2013 Design for X Page 48 24
Design for serviceability Ability to diagnose, remove, replace, replenish, or repair any component or subassembly to original specifications with relative ease Poor serviceability produces warranty costs, customer dissatisfaction, and lost sales and market share due to loss loyalty Have serviceability personnel involved in the early stages, as they are considered a customer segment. PEUSS 2012/2013 Design for X Page 49 Design for the environment Addresses environmental concerns as well as postproduction transport, consumption, maintenance, and repair The aim is to minimize environmental impact, including strategic level of policy decision-making and design development DFE usually comes with added initial cost, causing an increment of total life cost Economic evaluation is required both for maximum economic benefit and to estimate what the expected financial savings (or losses) will be PEUSS 2012/2013 Design for X Page 50 25
Design for life-cycle cost Real cost of the design Includes the associated costs of defects, litigations, buybacks, distributions support, warranty, and the implementation cost of all employed DFX methods Activity-based cost (ABC)* is a method for estimating life-cycle design cost ABC assumes that the design, whether a product, a service, or a process, consumes activities. ABC objective is to identify activities in the design life, and then assign reliable cost drivers and consumption intensities to the activities PEUSS 2012/2013 Design for X Page 51 26